Rates of Photosynthesis in Characean Cells

Abstract

Photosynthetic ¹⁴C fixation by Characean cells in solutions of high pH containing NaH¹⁴CO₃ gave a measure of the ability of these cells to take up bicarbonate (H¹⁴CO₃⁻). Whereas cells of Nitella translucens from plants collected and then stored in the laboratory absorbed bicarbonate at 1−1.5 μμmoles cm⁻² sec⁻¹, rates of 3−8 μμmoles cm⁻² sec⁻¹ were obtained with N. translucens cells from plants grown in the laboratory. Influxes of 5–6 μμmoles cm⁻² sec⁻¹ were obtained with Chara australis, 3–8 μμmoles cm⁻² sec⁻¹ with Nitellopsis obtusa, and 1−5 μμmoles cm⁻² sec⁻¹ with Tolypella intricata. It is considered that these influxes represent the activity of a bicarbonate pump, which may be an electrogenic process. In solutions of lower pH, H¹⁴CO₃⁻ uptake would be masked by rapid diffusion of ¹⁴CO₂ into the cells: the four Characean species fixed ¹⁴CO₂ at maximum rates of 30−40 μμmoles cm⁻² sec⁻¹ (at 21° C).